Hi, I though this was great! I really like the atmosphere of this game, especially the sound and character designs. I think it's got great potential! I have a list of things that I noticed while playing that I thought might be helpful.
1. Zoom level, at least when I play the game in chrome the window is bigger than my screen and I had to zoom out in the browser. Also in the actual window itself I felt a bit too zoomed in on the character so it became difficult to understand the environment around me.
2. Character Control, it seemed to me like you were using a physics based character controller (although I could be wrong here), this lead to a few things that felt a little clunky. e.g. sticking to walls, sliding off platforms , jerky movement when going up and down moving platforms. I think if you switched to a custom physics based controller you could get some more responsive movement. There's a unity tutorial for that here in case you're interested: https://bit.ly/2NyjDkz , but it might be a bit of work to switch (I had a similar problem when I tried making a platformer)
3. Navigation, because the camera is so tight on the character and the environment is dark, it's hard to know where to go, I found myself backtracking and going the wrong way very often which lead to frustration. I thought it might be good if there was some sort of mini map. Or a clearer indication we had already been to an area (maybe the towers, change colour...) Or simply a counter for how many notes we still need to collect in a level. I'm not sure what the best solution would be but in any case I think it's difficult to find your way around the levels and this could be improved.
4. Minor Points, 1. it's not clear which blocks are foreground and which you can actually stand on. This lead me to think I was stuck below in the first level when I fell down. (There's a block on the left that you can walk through but looks like it makes the platform too high to jump on). 2. A Sfx for collecting a note + one for collecting all the notes would be nice. 3. I also expected to immediately teleport back once I had collected all the notes, and I struggled to find the door, but I think that comes down to navigation again. 4. I also found that the ringing when text is sped up becomes a little grating. 5. Also a general point would be, I think it might be better to concentrate on one (or two) levels first (for a game jam at least), but make sure playing these feels really good, as I found the number of levels a bit too much, given some were a little frustrating to complete.
Most of these things come down to polish or quality of life stuff. I understand that it's still in development and I think that fundamentally it's got the components of a great game. I hope you find some of that feedback helpful. (Sorry for the big wall of text) :)